1. Field of the Invention
The invention relates to a seal for a door for a coke oven comprising an elongate knife edge element having a knife edge which, in the closed position of the door, engages a sealing surface on the surround of the coke oven opening, the knife-edge element being urged by pressing means against a sealing surface on the side of the door. The invention also relates to a coke oven door provided with such a seal and to a coke oven provided with the door.
2. Description of the Prior Art
A conventional seal of the above type is illustrated in FIG. 2 of the accompanying drawings and will be described in more detail below.
The purpose of this seal is to prevent leakage of gas from the coke oven to the atmosphere. Difficulty in sealing is primarily due to the frame of the coke oven and the frame of the door itself becoming deformed as a result of
(a) long term distortions during the life of the door and the oven and
(b) short term distortions arising during the heating of the coke oven in operation. Conventionally, leakages are dealt with by striking the back of the knife edge element at the point of the leak, so that it shifts relative to the door. This is an inconvenient and labour-intensive operation and it can be difficult to deal in this way with leaks which are the result of short-term distortion.
A considerable effort has been put, in recent years, into development of a membrane type seal, in which the knife edge element is not pressed against a sealing surface on the door, but is sealingly connected to the door by a resilient membrane. Such an arrangement may allow the knife edge element to be resiliently urged towards the sealing surface on the surround of the coke oven opening, but suffers the considerable disadvantages
(a) that there is still only a limited ability to accommodate deformations, e.g. a deformation of 20 mm only and
(b) that there is a high risk of damage of the thin membrane, bearing in mind that the door is very heavy and lacks accurate guidance and must also be vigorously cleaned.
The present invention is not concerned with membrane type seals, but with seals of the kind described at the beginning of this specification. U.S. Pat. No. 2,778,784 describes a seal of this kind in which the knife edge element is divided into a plurality of longitudinally extending parts which abut each other. The purpose of this is to increase the flexibility of the sealing element, so that it can better conform to the frame of the coke oven. The method illustrated for adjusting the element is striking it with a tool, as described above. The present applicants are not aware that a seal of this construction has ever been used in practice, and it can be seen to suffer from the disadvantage that the knife edge element can only be adjusted relative to the door over a limited distance. If the knife edge element is extended too far out from the door, in order to accommodate large distortions (e.g. 3 to 4 cm as may occur with a door 7 m in height), it will lose its support and its front portion will be liable to be displaced laterally, breaking the seal.
The object of the present invention is to provide a seal which is capable of accommodating large distortions of the coke oven frame and yet is simple and robust in construction. Preferably the seal is easily assembled and disassembled to and from its working position and preferably also it is self-adjusting so as to follow distortions which occur.
In the seal of the present invention, the knife edge element is, as in U.S. Pat. No. 2,778,784, divided into a plurality of abutting parts which extend longitudinally. Furthermore, holding means are provided to hold the parts against movement relative to each other in the adjustment direction and to restrain at least the outermost of the parts (i.e. the part which presses against the sealing surface on the surround of the coke oven opening) against movement relative to the door in the lateral direction. At the same time relative longitudinal sliding of the parts upon flexure of the knife edge element must be permitted. The lateral restraint of the outermost part is independent of the sealing surface on the side of the door against which the knife edge element is pressed.
In order to provide a structure which is easily assembled into the working position, the said holding means is preferably in the form of a plurality of brackets which are mounted on the knife edge element at longitudinally spaced points, each bracket embracing the parts of the knife edge element so as to prevent their movement apart in the adjustment direction, and being secured to one of the parts, preferably the outermost part.
In a preferred embodiment, the length, in the adjustment direction, of the said sealing surface on the door against which the knife edge element is urged by said pressing means, is less than 25% of the width of the knife edge element in the adjustment direction, and there are provided, spaced apart longitudinally along the knife edge element, a plurality of spring members which urge the knife edge element towards the sealing surface on the surround of the coke oven opening. The use of a narrow sealing surface on the door in this way is highly advantageous, because the surfaces at this seal tend to become dirtied by resinous products from the coal being coked in the oven. With a relatively small sealing surface, the resultant adhesive forces which tend to prevent movement of the knife edge element are much reduced. The important result is that it is therefore possible to use a plurality of spaced apart spring members to urge the knife edge element in the adjustment direction against the surround of the coke oven opening. In this way a self-adjusting seal can be made, which follows distortion of the surround. The unsatisfactory method of striking the seal to adjust it is thus rendered unnecessary. It has been found that the seal in accordance with the invention can be designed to easily follow bending of 40 mm, so that leaks resulting from short term distortion are also properly sealed. The seal according to the invention can be applied to existing coke ovens.